KR101440974B1 - Automatic inspection method for stain in the polarizing plate using color difference analysis - Google Patents

Abstract

The present invention relates to a method of automatically inspecting a polarizing plate stain using color difference analysis, comprising the steps of: (a) mounting an inspection polarizing plate or a polarizing element on at least one reference polarizing plate; (b) irradiating light to the subject polarizing plate or the polarizing element; (c) photographing the subject polarizing plate or the polarizing element; And (d) calculating a chrominance of each pixel using the data extracted from the image photographed in the step (c), and quantifying the degree of the smudge using the calculated chrominance data .

Description

[0001] The present invention relates to an automatic inspection method for stain in polarizing plate using color difference analysis,

The present invention relates to a method of automatically inspecting a polarizer unevenness, more specifically, it is possible to objectively determine the degree of unevenness of a polarizer using a color difference analysis, monitor whether a polarizer is defective in a production line in real time, And an automatic inspection method of a polarizing plate unevenness designed to automatically perform the quality inspection of the polarizing plate after the inspection.

The polarizing plate refers to an optical element used for transmitting light having a specific polarization direction to a liquid crystal display element. Generally, a polarizing plate is manufactured by dyeing, crosslinking, or stretching a PVA (polyvinyl alcohol) film.

Conventional general polarizing plate processes include a step of ion-plating a PVA film with iodine or a dye, a step of adding boric acid or the like to crosslink iodine or a dye to a PVA film, and a step of stretching a PVA film. The stretching step may be performed separately or simultaneously, and the order of each of these steps is not fixed. After completion of the step of dyeing, crosslinking and stretching of the PVA film, the PVA element is made by drying it. A polarizing plate is completed by adhering a protective film such as TAC (triacetyl cellulose) film to one side or both sides of the thus-produced PVA element using a PVA adhesive or the like.

However, the polarizing plate thus produced may have uneven streaks in the machine direction (MD) due to various causes such as uneven dyeing or adhesion failure in the manufacturing process. If such unevenness occurs, There arises a problem that the brightness is uneven and the final product is defective. Therefore, screening work for measuring the level of unevenness of the polarizing plate and selecting defective products is required. In general, the inspection of the stain of the polarizing plate is performed by visual inspection of the inspector. This method has a problem that it is difficult to produce a uniform quality product because the degree of defective product is determined according to the subject of the inspector.

Recently, a method of quantifying the level of unevenness of the polarizing plate has been sought. The results of the search are as follows: a) between the reference polarizing plates whose absorption axes are parallel to each other so that the absorption axis of the polarizing plate to be inspected is orthogonal to the absorption axis of the reference polarizing plate B) polarizing plate unevenness is quantitatively quantified by using brightness data among data obtained by photographing the polarizing plate to be inspected in the state that light is irradiated toward the polarizing plate to be inspected, and thereby the stain of the polarizing plate can be objectively inspected And a polarizing plate stain test method was developed.

However, in this technique, since the absorption axis of the reference polarizing plate and the polarizing plate to be inspected are orthogonal to each other, the amount of light transmitted through the polarizing plate to be inspected is extremely small, so that the exposure time of the imaging device becomes relatively long in order to obtain analytical image data, There is a problem in that there is a difference between the form of the smudge obtained by using the RGB data extracted from the shot image and the smudge form observed by the naked eye. In addition, in the related art, there has been a limit in that it is difficult to identify a stain due to a minute color difference because the stain is numerically calculated by calculating the intensity data from the data extracted from the photographed image.

Therefore, there has been a demand for development of a stain quantification and automatic inspection method of a polarizing plate capable of solving the above-mentioned problems.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a method and apparatus for analyzing an image of a polarized plate to be analyzed, And a method for automatically checking the unevenness of the polarizer using the color difference analysis.

To this end, the present invention provides, in one aspect, (a) a method comprising: (a) mounting a polarizing plate or polarizing element to be inspected between at least two reference polarizing plates having parallel absorption axes; (b) irradiating light to the subject polarizing plate or the polarizing element; (b-1) rotating the to-be-tested polarizing plate or the polarizing element such that a brightness of the target polarizing plate or the polarizing element is 5 to 10 nit; (c) photographing the subject polarizing plate or the polarizing element; And (d) calculating a chrominance of each pixel by using the data extracted from the image photographed in the step (c), and quantifying the degree of the stain using the calculated chrominance data. Provides an automatic inspection room for polarizer stains.

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The step (d) includes the steps of: (d-1) extracting data of each pixel constituting the image from the image photographed in the step (c); (d-2) setting an inspection region by grasping the position of each pixel from the data extracted in the step (d-1); (d-3) calculating chrominance of each pixel by grasping the color coordinates of each pixel from the data extracted in (d-1) in the inspection region set in the step (d-2); (d-4) averaging chrominance data of each pixel measured in the step (d-3) with respect to a machine direction (MD); (d-5) calculating a maximum color difference amplitude value by analyzing a value averaged in the step (d-4) in a transverse direction (TD); And (d-6) comparing the maximum color difference amplitude value calculated in the step (d-5) with the numerical data indicating the degree of the predetermined blob to quantify the degree of blob.

Here, the data of each pixel extracted in the step (d-1) preferably includes RGB data and position data.

Meanwhile, a data processing step is performed between the step (d-1) and the step (d-2) so that the contrast ratio of the RGB data among the data of each pixel extracted in the step (d-1) can do.

The data processing step may include: a data conversion step of converting the RGB data among the data of each pixel extracted in the step (d-1) into color, saturation, and contrast data; A data processing step of separating the contrast data from the converted data and performing a histogram equalization process; And a data re-conversion step of re-converting the contrast data subjected to the histogram equalization processing and the hue and saturation data into RGB data.

Meanwhile, the method for automatically checking the unevenness of the polarizer using the color difference analysis may further include visualizing the degree of the unevenness quantified in the step (d) after the step (d).

Using the automatic inspection method of polarizing plate stain using the color difference analysis of the present invention, it is possible to monitor the degree of stain of the polarizing plate in real time on a production line without human inspection of the polarizing plate, And the production efficiency is improved.

In addition, the automatic inspection method of polarizing plate unevenness using the color difference analysis of the present invention has an advantage that an image suitable for analyzing the unevenness can be easily obtained because the brightness of the polarizing plate to be inspected is kept within a certain range during photographing.

In addition, the method for automatically checking the polarizer plate using the color difference analysis of the present invention is advantageous in that fine speckles can be detected more accurately by processing the data extracted from the photographed image to have a high contrast ratio.

In addition, the method of automatically checking the unevenness of the polarizer using the color difference analysis of the present invention is advantageous in that the quality of the product is kept constant since the degree of stain of the polarizer is numerically evaluated through objective criteria.

FIG. 1 is a flowchart illustrating a method for automatically checking polarizer stains using color difference analysis according to an embodiment of the present invention. Referring to FIG.
FIG. 2 is a view illustrating an example of an inspection area set in the automatic inspection method of a polarizing plate stain using color difference analysis according to an embodiment of the present invention.
FIG. 3 is a graph showing a change in chrominance according to a transverse direction (TD) calculated by a method for automatically checking a polarizing plate stain using a color difference analysis according to an embodiment of the present invention.
4 is a view showing an example of an apparatus to which a polarizing plate unevenness automatic inspection method using a color difference analysis according to an embodiment of the present invention is applied.

Hereinafter, the present invention will be described more specifically with reference to the drawings.

It is to be understood, however, that the following description is made in order to provide a better understanding of the present invention, and is not to be construed as limiting the present invention. Also, in the following drawings, like reference numerals refer to like elements, and it is to be understood that elements shown in the drawings may be exaggerated, reduced or omitted for clarity.

FIG. 1 is a flowchart showing a flow of a method for automatically checking a polarizing plate stain using a color difference analysis according to the present invention, FIG. 2 is a view showing an example of an inspection area set in a polarizing plate stain automatic inspection method using a color difference analysis of the present invention, 3 is a graph showing a change in color difference according to a transverse direction (TD) calculated by a polarizing plate unevenness automatic inspection method using the color difference analysis of the present invention. FIG. 4 is a graph Is an example of a device to which the method is applied.

Referring to FIGS. 1 to 4, a polarizing plate unevenness inspection method using the color difference analysis according to the present invention includes a step S100 of mounting a polarizing plate to be inspected, a light irradiation step S200, a photographing step S300, a smear quantification step S400, .

The step S100 of inserting the polarizing plate to be inspected is a step of mounting the polarizing plate or the polarizing element 30 on the at least one reference polarizing plate 20.

Here, the reference polarizing plate 20 may be a polarizing plate, a polarizing plate, a polarizing element or the like commonly used in the related art. For example, a transparent TAC (Clear TAC) A UZ TAC of FUJIFILM CO., LTD.) Is used and a polarizing plate semi-finished product having a transmittance of 41.0 to 42.5% is used.

The reference polarizing plate 20 may be at least one, but it is more preferable that at least two reference polarizing plates 20 are used. In general, since the polarization can be changed by various factors, a polarizing component parallel to the absorption axis Because it can not absorb completely.

Here, when the reference polarizer 20 is at least two, it is preferable that the absorption axes of at least two reference polarizers 20 are parallel to each other. This makes it possible to maximize the absorption of the polarization component parallel to the absorption axis of the reference polarizing plate by using at least two reference polarizing plates whose absorption axes are parallel to minimize the components other than the polarization component parallel to the transmission axis of the polarized light component or the polarizing element This is because the visibility of the stain can be improved.

Meanwhile, the step of inserting the polarized light to be measured (S100) may be mounted on at least one reference polarizing plate (20), but it is more preferably mounted between at least two reference polarizing plates (20). This is to improve the visibility of the stain by increasing the absorption rate of the polarized component parallel to the absorption axis of the reference polarizing plate. Generally, polarized light can be changed by various factors, so even if a polarized component parallel to the absorption axis of the polarizing plate is able to transmit through the polarizing plate, a single polarizing plate can not completely absorb the polarized component parallel to the absorption axis. Therefore, by inserting a polarizing plate or polarizing element to be inspected between at least two reference polarizing plates, it is possible to maximize the absorption of the polarizing component parallel to the absorption axis of the reference polarizing plate and to provide a polarizing component other than the polarizing component parallel to the transmitting axis of the polarizing plate or polarizing element Thereby improving the visibility of the stain.

On the other hand, the polarizing plate or polarizing element 30 to be inspected is preferably such that the brightness thereof is preferably 2.5 to 20 nits (nit), more preferably 2.5 to 15 nits (nit) The absorption axis of the polarizing plate or the polarizing element 30 to be inspected is arranged so as to be inclined with respect to the absorption axis of the reference polarizing plate 20 in the inspection polarizing plate mounting step S100 so that the absorption axis of the polarizing plate 30 or the polarizing element 30 becomes 5 to 10 nit . Alternatively, the step of rotating the polarizer or the polarizing element to be inspected may further include, between the light irradiation step (S200) and the photographing step (300), the brightness of the mounted polarizer The test subject polarizing plate or the polarizing element 30 is rotated so as to be 20 nits (nit), more preferably 2.5 to 15 nits (nit), most preferably 5 to 10 nits (nit) The absorption axis of the inspection polarizing plate or the polarizing element 30 may be inclined with respect to the absorption axis of the reference polarizing plate 20. [

Here, the term "nit" refers to the surface brightness having a luminance of 1 cd / m ² or 0.00001 sb as a unit of luminance, and is inclined to the absorption axis of the subject polarizing plate or the polarizing element and the absorption axis of the reference polarizing plate so as to have a predetermined luminance range The arrangement is to easily obtain an image capable of analyzing the stain. Specifically, when the luminance of the mounted polarizer or polarizer is less than 2.5 nits (liters), the amount of light passing through the polarizer or the polarizer is extremely small, so it takes a considerable time to obtain an image capable of analyzing the blur And when it exceeds 20 nits (nit), the amount of light passing through the polarizing plate or the polarizing element to be inspected becomes too large, and it becomes difficult to precisely photograph the shape of the polarizing plate. As a result, it becomes difficult to accurately detect the unevenness of the polarizing plate . Further, when the absorption axis of the reference polarizing plate is orthogonally arranged with respect to the absorption axis of the target polarizing plate or the polarizing element as in the prior art, even when the light is irradiated from the light source toward the target polarizing plate, the amount of light passing through the target polarizing plate is extremely small, It is preferable that the absorption axis of the reference polarizing plate and the absorption axis of the polarizing plate or the polarizing plate to be inspected are inclined so as to secure a constant amount of light.

Next, the light irradiation step (S200) is a step of irradiating light to the subject polarizing plate or the polarizing element (30). In this case, the light source unit 10 used for the light irradiation may be a backlight unit or an LED light source generally used in a display device, and the lower part of the polarized light or polarized light 30 to be inspected, that is, Is located on the rear surface of the element (30). It is preferable that the intensity of the light source means 10 is set to be 2.5 to 20 nits (nits) upon irradiation of the polarizing plate or polarizing element to be inspected.

Next, the photographing step S300 is a step of photographing the polarizing plate or the polarizing element to be inspected. At this time, the photographing means 50 is located at the front of the subject polarizing plate or the polarizing element 30, that is, the front face of the subject polarizing plate or the polarizing element 30, and may be a general digital camera, a CCD camera,

Next, the smear quantification step S400 extracts data from the photographed image in the photographing step S300, calculates a color difference using the extracted data, and calculates a degree of smear using the calculated color difference data . This process is generally performed by a computing means 60 such as a computer.

Here, the smear quantification step (S400) proceeds in the following order. First, data of each pixel constituting the image is extracted from the image photographed in the photographing step S300. Here, the data of each pixel includes position data and RGB data (S410).

Next, in step S420, a data processing step of processing the data of each pixel extracted in step S410 so that the contrast ratio of the RGB data is high may be included.

The data processing step S420 includes a data conversion step S421, a data processing step S422, and a data re-conversion step S423.

The data conversion step S421 is a step of converting the RGB data among the data of each pixel extracted in step S410 into hue, saturation, and contrast data (HSI data) Because.

Meanwhile, the data processing step S422 extracts the contrast data from the data converted in the data conversion step S421 and performs histogram equalization processing. Here, the histogram equalization is a process of uniformly rendering an image having a poor contrast distribution by adjusting the histogram of the darkly photographed image, maximizing the contrast by redistributing the brightness distribution of the image, and the histogram equalization process is known It proceeds according to the method.

Meanwhile, the data re-conversion step S423 is a step of combining the lightness and darkness data obtained by performing the histogram equalization in the lightness data extraction step S422 and combining the color and saturation data into RGB data.

Next, the position of each pixel is determined from the data extracted in step S410, and an inspection area is set (S430). That is, the inspection area is set using the position data of each pixel.

Here, as shown in FIG. 2, it is preferable that the inspection area includes pixels of 1/10 or less of the number of pixels for the machine direction (MD) of the photographed image. This is to detect and quantify even the minute spot A. If the inspection area exceeds 1/10 of the number of pixels for the machine direction (MD, machine direction) of the polarizing plate or the polarizing element to be inspected, it becomes difficult to obtain a valid value for fine stain.

In addition, it includes at least 10 pixels, preferably 100 or more pixels in the machine direction (MD) of the photographed image. This is to ensure efficiency in quantifying fine stains.

Next, in step S430, the color coordinates of each pixel are obtained from the data extracted in step S410, and the color difference of each pixel is measured in step S440. In other words, the color coordinates of each pixel are calculated by grasping the color coordinates from the RGB data of each pixel in the inspection region.

Specifically, the color difference calculation process checks the color coordinates (e.g., CIELAB's color coordinates (L ^* , a ^* , b ^* )) of all the pixels in the entire area of the photographed image, sets the mode as the reference value _{^{L 1 *, a 1 *,}} b 1 *)), the set all of the pixels (color coordinates of the pixels (L ₂ in the inspection area _{^{*, a 2 *, b 2}} *)) calculates the color difference according to the following formula 1 for do.

[Formula 1]

Here, the color coordinates of the reference value are (L ₁ ^* , a ₁ ^* , b ₁ ^* ), the color coordinates (L ₂ ^* , a ₂ ^* , b ₂ ^* ) of each pixel, and ΔE _ab ^* to be.

Next, the chrominance data of each pixel calculated in step S440 is averaged with respect to the machine direction (MD) (S450). This means that the color difference values of the respective columns in the inspection region are averaged.

Next, in step S460, the maximum color difference amplitude value is calculated by analyzing the average value of the chrominance averaged in step S450 in the transverse direction (TD). At this time, the local maximum and minimum values are checked while checking the average value of the chrominance in the transverse direction (TD), and when the amplitude value of the local chrominance is larger than the predetermined threshold value, the value is stored and stored Value is used to calculate the maximum color difference amplitude value. Here, the predetermined threshold value may be any value, but generally refers to a maximum amplitude value that can be judged as noise.

Next, the maximum color difference amplitude value calculated in step S460 is compared with the numerical data indicating the degree of the predetermined smear to match the degree of smear of the polarizing plate or polarizing element to be inspected (S470). As an example of numerical data representing the degree of the predetermined smudge, numerical data is 5, 5 to 8, 3, 9 to 12, 3, 13 to 16 when the size of the maximum color difference amplitude value is 0 to 4 , And when the number is 17 or more, the numerical data can be set to 1. Here, 5 of the numerical data corresponds to a case where no unevenness is observed when viewed with naked eyes, and 1 corresponds to a case where unevenness is most severe when observed with naked eyes.

Meanwhile, in the method for automatically checking the unevenness of the polarizer using the color difference analysis of the present invention, after the step S470, the numerical data quantified in the step S470 may be visualized. Here, the means for visualizing the numerical data may be a display such as a monitor or the like.

According to the above-described automatic method for checking the unevenness of the polarizer using the color difference analysis of the present invention, the brightness of the polarizing plate to be inspected can be secured within a certain range at the time of photographing so that an image suitable for analyzing the stain can be easily obtained, The fine stain can be detected more accurately, and the degree of staining of the polarizing plate is numerically quantified through objective criteria, so that the quality of the product can be kept constant.

Hereinafter, the present invention will be described in more detail with reference to specific examples.

[Example 1]

The unstretched PVA film was dyed at a salt-bath temperature of 25 to 30 ° C and a residence time of 1 to 5 minutes, and then stretched to 5 to 6 times to prepare a polarizing element. The protective film of the polarizing element was a protective film having a thickness of 80 mu m and haze in UZ Grade.

The thus prepared polarizing plate was mounted on a reference polarizing plate (manufactured by LG Chemical, RB60SR10, unit permeability: 39.7%), and then irradiated with a 42-inch backlight (LG Display, color temperature 10,000K). At the time of light irradiation, the absorption axis of the prepared polarizing plate is inclined to the absorption axis of the reference polarizing plate such that the brightness of the polarizing plate is 5 nit. Thereafter, the image was photographed by a digital camera (Nikon, D3100 Zoom lens) on the backlight, and the photographed image was transferred to a computer. The computer extracts data of each pixel from the transmitted image, converts RGB data among the extracted data into hue, contrast, and saturation data (HSI data), extracts contrast data from the converted HSI data, After the processing, the HSI data was converted back to RGB data by combining the equalized lightness data and the hue and saturation data. The entire image having the number of pixels of 4608X3000 is divided into ten regions, the chrominance of all 4608X300 pixels in each inspection region is calculated, the chrominance values of 300 pixels in the machine direction are averaged, The average color difference value of each pixel is analyzed to calculate and store the maximum amplitude value in the inspection region, and the stored values are visualized. The program used here was based on a source made with Image J and C ++. In addition, the degree of staining was quantified by comparing the stored maximum amplitude value with numerical data indicating the degree of predetermined staining. The preset numerical data were set to 5, 5 to 8, 4 to 9 to 12, 2 to 13 to 16, and 1 to 17, respectively. 5 of the numerical data corresponds to a case in which no unevenness is observed in the naked eye, and 1 corresponds to a case in which unevenness in the naked eye is most severe. Table 1 shows the maximum amplitude value and the degree of staining of the polarizing plate to be inspected.

[Example 2]

A polarizing plate was manufactured in the same manner as in Example 1 except that a compensating film made of WVEA (manufactured by Fuji Photo Film Co., Ltd.) and UZ Clear TAC (manufactured by Fuji Photo Film Co., Ltd.) The polarizer was calculated in the same manner as in Example 1, and the degree of staining was quantified. Table 1 shows the maximum amplitude value and the degree of staining of the polarizing plate to be inspected.

[Example 3]

A polarizing plate was prepared in the same manner as in Example 1 except that the type of the film for protecting the polarizing element was changed to UZ and UZ Clear 60 탆. The polarizing plate thus prepared was subjected to the same calculation as in Example 1, The degree of staining was quantified. Table 1 shows the maximum amplitude value and the degree of staining of the polarizing plate to be inspected.

[Example 4]

A polarizing plate was prepared in the same manner as in Example 1, except that the type of the film for protecting the polarizing element was changed to Hard Coating Grade (Konica Co., Ltd.) and UZ Clear 40 μm (manufacturer: Konica Corp.) The polarizer was calculated in the same manner as in Example 1, and the degree of staining was quantified. Table 1 shows the maximum amplitude value and the degree of staining of the polarizing plate to be inspected.

[Example 5]

The unstretched PVA film was dyed at a salt-bath temperature of 25 to 30 ° C and a residence time of 1 to 5 minutes, and then stretched to 5 to 6 times to prepare a polarizing element. The protective film of the polarizing element was made of WVEA and UZ haze, and a film having a thickness of 60 μm was used. The thus-prepared polarizing plate was subjected to calculation of the amplitude in the same manner as in Example 1, and the degree of staining was quantified. Table 1 shows the maximum amplitude value and the degree of staining of the polarizing plate to be inspected.

Color difference maximum amplitude value A number indicating the degree of staining Example 1 9.28 3 Example 2 6.32 4 Example 3 3.82 5 Example 4 23.63 One Example 5 12.78 2

According to Table 1, it can be confirmed that the degree of the smear is quantified by using the maximum amplitude value calculated by the polarizing plate automatic smear check method using the color difference analysis of the present invention. In addition, since the degree of staining thus quantified corresponds to the degree of staining observed with the naked eye, the maximum amplitude value measured by the method of the present invention has an effect that it can represent the visibility of the polarizing plate unevenness (stripe).

10 light sources
20 reference polarizer
30 Inspection Polarizer or Polarizer
50 photographing device
60 operating means
70 display
A stain

Claims (16)

(a) mounting a polarizing plate or polarizing element to be inspected between at least two reference polarizing plates whose absorption axes are parallel;
(b) irradiating light to the subject polarizing plate or the polarizing element;
(b-1) rotating the to-be-tested polarizing plate or the polarizing element such that a brightness of the target polarizing plate or the polarizing element is 5 to 10 nit;
(c) photographing the subject polarizing plate or the polarizing element; And
(d) calculating a chrominance of each pixel by using the data extracted from the image photographed in the step (c), and quantifying the degree of the stain using the calculated chrominance data, Automatic inspection method of stains.
delete delete delete delete delete delete delete delete delete delete The method of claim 1, wherein the step (d)
(d-1) extracting data of each pixel constituting the image from the image photographed in the step (c);
(d-2) setting an inspection region by grasping the position of each pixel from the data extracted in the step (d-1);
(d-3) calculating chrominance of each pixel by grasping the color coordinates of each pixel from the data extracted in (d-1) in the inspection region set in the step (d-2);
(d-4) averaging the chrominance data of each pixel calculated in the step (d-3) with respect to the machine direction (MD);
(d-5) calculating a maximum color difference amplitude value by analyzing a value averaged in the step (d-4) in a transverse direction (TD); And
(d-6) quantifying the degree of smear by comparing the maximum color difference amplitude value calculated in the step (d-5) with numerical data representing the degree of predetermined smear, Way.
The method of claim 12, wherein the data of each pixel extracted in step (d-1) is subjected to color difference analysis including RGB data and position data.
14. The method of claim 13, further comprising, between (d-1) and (d-2)
And a data processing step of processing the data of each pixel extracted in the step (d-1) so that the contrast ratio of the RGB data is high.
15. The method according to claim 14,
A data conversion step of converting the RGB data among the data of each pixel extracted in the step (d-1) into color, saturation, and contrast data;
A data processing step of separating the contrast data from the converted data and performing a histogram equalization process; And
And a data re-conversion step of re-converting the histogram equalized lightness data and the hue and saturation data into RGB data.
The method of claim 1, further comprising the step of visualizing the degree of staining quantified in the step (d) after the step (d).

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